Packet Delay Minimization in Multi-hop Wireless Sensor Networks with Periodic Traffic

The paper is devoted to minimization of end-to-end packet delay in multi-hop TDMA-based wireless sensor networks composed of gateways and wireless routers that form a mesh topology. The network is supposed to deliver packets, generated at the sensors, to the gateways. It is assumed that each sensor (connected to one of the routers) produces a new packet at the beginning of each consecutive TDMA frame, and each such packet is then transmitted to a given subset of gateways along a multicast routing tree rooted at the sensor's router. Assuming that the transmission pattern of the TDMA frame is given (i.e., knowing what nodes are selected to broadcast in each time slot of the frame) and sufficient to carry the so described packet streams with finite delay, we aim at finding a packet broadcast scheduling pattern that minimizes the maximum packet delay over all packet streams generated by the sensors. To achieve that, we introduce an exact mixed-integer programming formulation for the related optimization problem. Since the problem formulation can be effectively solved only for networks of limited size, we propose a relevant heuristic method, and demonstrate, through an extensive numerical study, its capability of finding near optimal solutions in reasonable time.